Electrolyte materials for use in electrochemical cells

ABSTRACT

Electrolyte materials for use in electrochemical cells, electrochemical cells comprising the same, and methods of making such materials and cells, are generally described. In some embodiments, the materials, processes, and uses described herein relate to electrochemical cells comprising sulfur and lithium such as, for example, lithium sulfur batteries.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/216,538, filed Aug. 24, 2011, which claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application Ser. No. 61/376,559, filedAug. 24, 2010, which are incorporated herein by reference in theirentirety for all purposes.

FIELD OF INVENTION

Electrolyte materials for use in electrochemical cells, electrochemicalcells comprising the same, and methods of making such materials andcells are generally described. In some embodiments, the materials,processes, and uses described herein relate to electrochemical cellscomprising sulfur and lithium such as, for example, lithium sulfurbatteries.

BACKGROUND

Lithium compound containing electric cells and batteries containing suchcells are modern means for storing energy. They exceed conventionalsecondary batteries with respect to capacity and life-time and, in manytimes, use of toxic materials such as lead can be avoided. However, incontrast to conventional lead-based secondary batteries, varioustechnical problems have not yet been solved.

Secondary batteries based on cathodes based on lithiated metal oxidessuch as LiCoO₂, LiMn₂O₄, and LiFePO₄ are well established, see, e.g., EP1 296 391 A1 and U.S. Pat. No. 6,962,666 and the patent literature citedtherein. Although the batteries mentioned therein exhibit advantageousfeatures, they are limited in capacity. For that reason, numerousattempts have been made to improve the electrode materials. Particularlypromising are so-called lithium sulfur batteries. In such batteries,lithium will be oxidized and converted to lithium sulfides such asLi₂S_(8-a), a being a number in the range from zero to 7. Duringrecharging, lithium and sulfur will be regenerated. Such secondary cellshave the advantage of a high capacity.

A particular problem with lithium sulfur batteries is the thermalrunaway which can be observed at elevated temperatures between, e.g.,150 to 230° C. and which leads to complete destruction of the battery.Various methods have been suggested to prevent such thermal runaway suchas coating the electrodes with polymers. However, those methods usuallylead to a dramatic reduction in capacity. The loss in capacity has beenascribed—amongst others—to formation of Lithium dendrites duringrecharging, loss of sulfur due formation of soluble lithium sulfidessuch as Li₂S₃, Li₂S₄ or Li₂S₆, polysulfide shuttle, change of volumeduring charging or discharging and others.

In WO 2008/070059 various materials are disclosed for coating electrodesfor lithium sulfur batteries. However, the thermal runaway problem hasnot been solved satisfactorily.

SUMMARY OF THE INVENTION

Electrolyte materials for use in electrochemical cells, electrochemicalcells comprising the same, and methods of making such materials andcells, are provided. The subject matter of the present inventioninvolves, in some cases, interrelated products, alternative solutions toa particular problem, and/or a plurality of different uses of one ormore systems and/or articles.

In one aspect, an electrochemical cell (e.g., a lithium battery) isprovided. In some embodiments, the electrochemical cell (e.g., lithiumbattery) comprises an anode comprising lithium as the anode activespecies; a cathode comprising a cathode active species; and anelectrolyte comprising a non-fluid material positioned between the anodeand the cathode, and an auxiliary material absorbed by the non-fluidmaterial, the non-fluid material having a surface in contact with asurface of the anode. In some embodiments, the non-fluid material, incombination with the absorbed auxiliary material, has a yield strengthgreater than that of lithium metal. In some embodiments, the cathodecomprising the cathode active species may be supported by a cathodecurrent collector.

In some embodiments, the electrochemical cell comprises an anodecomprising lithium as the anode active species; a cathode comprising acathode active species; and an electrolyte comprising a non-fluidmaterial, wherein, when the electrochemical cell is configured for use,the electrolyte has a yield strength greater than that of lithium metal.

In some embodiments, the electrochemical cell comprises:

(A) an electrode containing sulfur

(B) an electrode containing lithium or a lithium alloy,

(C) at least one organic (co)polymer selected from polyethersulfones,said polyethersulfone being in the gel state,

(D) at least one organic solvent, and

(E) at least one salt of lithium.

In some embodiments, the electrochemical cell comprises an anodecomprising lithium as the active anode species; a cathode comprising acathode active species; and an electrolyte comprising a non-fluid (e.g.,solid) material, wherein when the electrolyte is configured such thatthe electrochemical cell can be cycled at a temperature of up to about130° C. without experiencing thermal runaway.

In some embodiments, a process for making an electrochemical cell isdescribed. The process for making the electrochemical cell can compriseproviding lithium or lithium alloy, which may be deposited on asubstrate, depositing a solution of at least one polyethersulfone in anorganic solvent on said lithium or lithium alloy, adjusting the residualsolvent content of polyethersulfone to a range of from 0.01 to 25% byweight, and treating said deposited polyethersulfone with a solution ofat least one salt of lithium in at least one organic solvent.

Furthermore, in another aspect, the present invention relates to amethod for making electrodes. Furthermore, in yet another aspect, thepresent invention relates to a process for using inventive batteries.

Other advantages and novel features of the present invention will becomeapparent from the following detailed description of various non-limitingembodiments of the invention when considered in conjunction with theaccompanying figures. In cases where the present specification and adocument incorporated by reference include conflicting and/orinconsistent disclosure, the present specification shall control. If twoor more documents incorporated by reference include conflicting and/orinconsistent disclosure with respect to each other, then the documenthaving the later effective date shall control.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting embodiments of the present invention will be described byway of example with reference to the accompanying figures, which areschematic and are not intended to be drawn to scale. In the figures,each identical or nearly identical component illustrated is typicallyrepresented by a single numeral. For purposes of clarity, not everycomponent is labeled in every FIGURE, nor is every component of eachembodiment of the invention shown where illustration is not necessary toallow those of ordinary skill in the art to understand the invention. Inthe figures:

FIG. 1 includes an exemplary schematic diagram of an electrochemicalcell, according to one set of embodiments.

DETAILED DESCRIPTION

Electrolyte materials for use in electrochemical cells, electrochemicalcells comprising the same, and methods of making such materials andcells, are generally described. In some embodiments, the materials,processes, and uses described herein relate to electrochemical cellscomprising sulfur and lithium such as, for example, lithium sulfurbatteries. The electrolyte can comprise a polymeric material and, insome cases, an absorbed auxiliary material. For example, the electrolytematerial can be capable of forming a gel, and the auxiliary material cancomprise an electrolyte solvent. In some instances, the electrolytematerial can comprise at least one organic (co)polymer selected frompolyethersulfones, polyvinylalcohols (PVOH) and branched polyimides(HPI). The non-fluid material in the electrolyte, when configured foruse, can, alone or in combination with the optional absorbed auxiliarymaterial, have a yield strength greater than that of lithium metal, insome embodiments.

One objective of the present invention is to provide an electrochemicalcell in which thermal runaway is mitigated while maintaining thecapacity of the cell. The inventors have discovered, within the contextof the invention, that this objective can be met by incorporating thematerials described herein (e.g., polymeric materials such as thosecapable of forming gels) into the electrolyte of the electrochemicalcell.

The materials for use in the electrolyte described herein can, in someembodiments, withstand the application of a force to the electrochemicalcell without sacrificing system performance. U.S. Patent Publication No.2010/0035128 to Scordilis-Kelley et al. filed on Aug. 4, 2009, entitled“Application of Force in Electrochemical Cells,” describes theapplication of forces in electrochemical cells for improved electrodechemistry, morphology, and/or other characteristics, which can improveperformance. The present invention involves, in one aspect, therecognition that the use of particular materials in the electrolyte canallow for the application of a force to an electrochemical cell withoutsacrificing the structural integrity of the cell. In addition, thematerials for use in the electrolyte described herein can withstandrepeated charging and discharging of the electrochemical cell in whichit is located, without producing a short circuit within the cell (e.g.,due to dissolution and re-plating of electrode materials).

The inventive electrochemical cell arrangements and materials describedherein can be used in primary batteries or in secondary batteries, whichcan be charged and discharged numerous times. In some embodiments, thematerials, systems, and methods described herein can be used inassociation with lithium batteries (e.g., lithium-sulfur batteries).According to the present invention the term “electrochemical cell”comprises primary and secondary electrochemical cells. Anelectrochemical cell comprises at least two electrodes, the cathode andthe anode. The cathode is the positive electrode, the anode is thenegative electrode. According to the present invention the cathoderefers to the electrode where the reduction takes place duringdischarge. The anode refers to the electrode where oxidation takes placeduring discharge.

Inventive batteries can contain electrochemical cells that are differentor identical.

Although the present invention can find use in a wide variety ofelectrochemical devices, an example of one such device is provided inFIG. 1 for illustrative purposes only. FIG. 1 includes a schematicillustration of an electrochemical cell 10 comprising a cathode 12 andan anode 14. In addition, the electrochemical cell comprises electrolyte16. The electrolyte can include one or more components inelectrochemical communication with the cathode and the anode. While theanode, cathode, and electrolyte in FIG. 1 are shown as having a planarconfiguration, other embodiments may include non-planar configurations(e.g., cylindrical, serpentine, etc.). In the set of embodimentsillustrated in FIG. 1 , electrochemical cell 10 also includes a housingstructure 17.

In some embodiments, cathode 12 and/or anode 14 can comprise at leastone active surface. As used herein, the term “active surface” is used todescribe a surface of an electrode that is in physical contact with theelectrolyte and at which electrochemical reactions may take place. Forexample, cathode 12 can include cathode active surface 18 and/or anode14 can include anode active surface 20.

Of course, the orientation of the components can be varied, and itshould be understood that there are other embodiments in which theorientation of the layers is varied. Additionally, non-planararrangements, arrangements with proportions of materials different thanthose shown, and other alternative arrangements are useful in connectionwith the present invention. A typical electrochemical cell also wouldinclude, of course, current collectors, external circuitry, and thelike. Those of ordinary skill in the art are well aware of the manyarrangements that can be utilized with the general schematic arrangementas shown in the figures and described herein.

The cathode can comprise a variety of cathode active materials. As usedherein, the terms “cathode active material” and “cathode active species”both refer to any electrochemically active species associated with thecathode. For example, the cathode may comprise a sulfur-containingmaterial, wherein sulfur is the cathode active material In oneembodiment of the present invention, cathode 12 contains from about 20%to about 90% sulfur or from about 50% to 80% sulfur, by weight. In someembodiments, the cathode active species comprises elemental sulfur.

In addition to the cathode active material (e.g., sulfur), cathode 12can further contain a binder. In some embodiments, the binder can be apolymeric binder such as polyvinyl alcohol, polyacrylonitrile,polyvinylidene fluoride, polyvinyl fluoride, polytetrafluoroethylene,copolymers from tetrafluoroethylene and hexafluoro propylene, copolymersfrom vinylidene fluoride and hexafluoro propylene or copolymers fromvinylidene fluoride and tetrafluoroethylene. In some embodiments of thepresent invention, cathode 12 contains from about 1% to about 20%binder, from about 1% to about 10% binder, or from about 1% to about 5%binder, by weight.

For the purpose of the present invention, vinylidene fluoride can alsobe referred to as vinylidene difluoride, and polyvinylidene fluoride canalso be referred to as polyvinylidene difluoride.

The cathode can further comprise a conductivity enhancing material. Insome embodiments, the cathode can contain carbon in an electricallyconductive form such as graphite, carbon fibers, carbon nanotubes,carbon black, and/or soot (e.g., lamp soot or furnace soot). In oneembodiment of the present invention, cathode 12 contains from about 10%to about 45%, by weight, conductivity enhancing material (e.g., carbonin its electricity conducting phase), or from about 20% to about 40% byweight.

Referring back to FIG. 1 , the electrochemical cell can also comprise ananode 14. The anode may comprise a variety of anode active materials. Asused herein, the terms “anode active material” and “anode activespecies” both refer to any electrochemically active species associatedwith the anode. For example, the anode may comprise a lithium-containingmaterial, wherein lithium is the anode active material. In someembodiments, the anode active species comprises lithium metal. In someembodiments, the anode active species comprises a lithium alloy.

The use of lithium in rechargeable batteries is known. Lithium can becontained as one film or as several films, optionally separated by aceramic material. Suitable ceramic materials include silica, alumina, orlithium containing glassy materials such as lithium phosphates, lithiumaluminates, lithium silicates, lithium phosphorous oxynitrides, lithiumtantalum oxide, lithium aluminosulfides, lithium titanium oxides,lithium silcosulfides, lithium germanosulfides, lithium aluminosulfides,lithium borosulfides, and lithium phosphosulfides, and combinations oftwo or more of the preceding.

Suitable lithium alloys for use in the embodiments described herein caninclude alloys of lithium and aluminum, magnesium, silicium and/or tin.

Referring back to FIG. 1 , electrochemical cell 10 can also include anelectrolyte 16, positioned between cathode 12 and anode 14. Theelectrolyte can include, in some embodiments, a non-fluid materialpositioned between the anode and the cathode. As used herein, the term“fluid” generally refers to a substance that tends to flow and toconform to the outline of its container during the time over which it isadded to the container. Examples of fluids include liquids and gases.

In some cases, the electrolyte can also include an auxiliary materialabsorbed by the non-fluid material. A first material is said to be“absorbed” in a second material when the first material does not freelyflow through the second material, but rather, is retained within thesecond material over the time scale in which it is added to the secondmaterial, i.e., it is substantially retained by the second material atleast (and in many embodiments, significantly longer) over a period oftime equivalent to the time consumed by fully adding/integrating thefirst material to the second material. “Retained,” in this context,means held within the second material by chemical attraction includinghydrogen bonding, Van der Waals interactions, ionic bonding, and thelike.

In some embodiments, the non-fluid material within the electrolyte canbe electrochemically active (i.e., can facilitate the exchange of ionsbetween the anode and the cathode). In some cases, the non-fluidmaterial within the electrolyte is not electrochemically active, and theelectrolyte includes an electrochemically active auxiliary material(e.g., an electrochemically active electrolyte fluid). In still otherembodiments, the electrolyte can include an electrochemically activenon-fluid material and an electrochemically active auxiliary material.

The non-fluid material may comprise a polymer and/or a copolymer, insome cases an organic polymer and/or copolymer. According to someembodiments, the polymers and copolymers are selected frompolyvinylalcohols and copolymers thereof, polyethersulfones andcopolymers thereof and branched polyimides and copolymers thereof.

The electrolyte can include a gel, in some cases. As used herein, theterm “gel” refers to a three-dimensional network comprising a liquid anda binder component, in which the liquid is entrained by and not allowedto flow through the binder. Gels can be formed when liquids areentrained within a three-dimensional network of solids upon applying theliquid to the solid network. In some cases, the three-dimensionalnetwork within a gel can comprise a liquid entrained within a polymer(e.g., a cross-linked polymer). One of ordinary skill in the art wouldbe capable of determining the difference between a gel and othercombinations of a solid and a fluid (e.g., a porous separator and aliquid solvent) by measuring, for example, the absorption stiffness ofthe gel via a dibutyl phthalate (DBP) uptake test. For this test, a drysample of the binder material is weighed. The weighed sample is immersedin DBP for 30 min. The excess DBP is removed by absorbent paper (e.g.kimwipe commercially available from Kimberly-Clark) and the sample isweighed again. Generally, upon exposure of the binder component of a gelto a liquid, the weight of the gel will increase, while the weight of aporous separator will not substantially increase. In some embodiments,the binder component of the gel is able to take up liquid in thesubstantial absence of pores greater than about 10 microns or greaterthan about 1 micron. The binder component of a gel can be substantiallyfree of pores in some cases.

In the context of the present invention, polyethersulfones are definedas polymeric materials that exhibit SO₂ groups (sulfonyl groups) andoxygen atoms that form part of ether groups in their constitutionalrepeating units. Polyethersulfones can be aliphatic, cycloaliphatic oraromatic polyethersulfones.

In one embodiment of the present invention, polyethersulfones areselected from polyethersulfones that can be described by the followingformula:

The integers can have the following meanings:

t, q independently 0, 1, 2 or 3,

Q, T, Y: each independently a chemical bond or group selected from —O—,—S—, —SO₂—, S═O, C═O, —N═N—, —R¹C═CR², —CR³R⁴—, where R¹ and R² are eachindependently a hydrogen atom or a C₁-C₁₂-alkyl group, and R³ and R⁴ aredifferent or identical and independently a hydrogen atom or aC₁-C₁₂-alkyl, C₁-C₁₂-alkoxy or C₆-C₁₈-aryl group, where R³ and R⁴ alkyl,alkoxy, or aryl can be substituted independently by fluorine and/orchlorine or where R³ and R⁴, combine with the carbon atom linking themto form C₃-C₁₂-cycloalkyl optionally substituted by one or moreC₁-C₆-alkyl groups, at least one of Q, T and Y being other than —O— andat least one of Q, T and Y being —SO₂—, and

Ar, Ar¹: independently C₆-C₁₈-arylene optionally substituted byC₁-C₁₂-alkyl, C₆-C₁₈-aryl, C₁-C₁₂-alkoxy, or halogen.

Q, T and Y can therefore each independently be a chemical bond or one ofthe above mentioned atoms or groups, in which case “a chemical bond” isto be understood as meaning that, in this case, the left-adjacent andright-adjacent groups are directly linked to each other via a chemicalbond. In accordance with the present invention, at least one element ofQ, T and Y is other than —O— and at least one element from Q, T and Y is—SO₂—. In a one set of embodiments, Q, T and Y are each independently—O— or —SO₂—.

Suitable C₁-C₁₂-alkyl groups comprise linear and branched, saturatedalkyl groups having from 1 to 12 carbon atoms. The following radicalsmay be included in particular: C₁-C₆-alkyl, such as methyl, ethyl,n-propyl, iso-propyl, n-butyl, sec-butyl, 2- or 3-methylpentyl andlonger-chain radicals such as non-branched heptyl, octyl, nonyl, decyl,undecyl, lauryl, and the singly or multiply branched analogues thereof.

When Ar and/or Ar¹ is/are substituted with C₁-C₁₂-alkoxy, theabove-defined alkyl groups having from 1 to 12 carbon atoms areespecially useful as the alkyl component in the alkoxy groups. Suitablecycloalkyl groups comprise in particular C₃-C₁₂-cycloalkyl groups, forexample cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl,cyclooctyl, cyclopropylmethyl, cyclopropylethyl, cyclopropylpropyl,cyclobutylmethyl, cyclobutylethyl, cyclopentylethyl, cyclopentylpropyl,cyclopentylbutyl, cyclopentylpentyl, cyclopentylhexyl, cyclohexylmethyl,cyclohexyldimethyl, cyclohexyltrimethyl.

Useful C₆-C₁₈-arylene groups Ar and Ar¹ include in particular phenylenegroups, especially 1,2-, 1,3- and 1,4-phenylene, naphthylene groups,especially 1,6-, 1,7-, 2,6- and 2,7-naphthylene, and also the bridginggroups derived from anthracene, phenanthrene and naphthacene. In somecases, Ar¹ is unsubstituted C₆-C₁₂-arylene, i.e., phenylene, especially1,2-, 1,3- or 1,4-phenylene, or naphthylene.

In some embodiments, the polyethersulfone can be a polysulfone, e.g.alkylated, such as methylated polycondensation products of the disodiumsalt of bisphenol A and 4,4′-dichlorodiphenyl sulfone,

Further examples of polyethersulfones are polyarylethersulfones, such aspolycondensation products of

with HCl having been split of during polycondensation or thepolycondensation products of 4,4′-dihydroxydiphenyl sulfone or itsdisodium salt and 4,4′-dichlorodiphenyl sulfone

Further examples of polyethersulfones are polyphenylsulfones, especiallythose made from 4,4′-biphenol and 4,4′-dichlorodiphenyl sulfone.

Hydroxyl groups in polyethersulfone can be free hydroxyl groups, therespective alkali metal salts, or alkyl ethers such as the respectivemethyl ethers.

In some embodiments, polyethersulfone can be a linear polyethersulfone.

In a special embodiment of the present invention, polyethersulfone canbe selected from branched polyethersulfones.

In one embodiment, the electrolyte material contains a mixture or blendof at least two of the polyethersulfones mentioned above, or a blend ofpolyethersulfone and an additional (co)polymer. In another embodimentthe electrode (B) comprises a blend from polyethersulfone (C) and anadditional (co)polymer (F).

In one embodiment of the present invention, polyether sulfone is appliedas a blend from polyethersulfone and an additional (co)polymer. Suitable(co)polymers can be any (co)polymers that are compatible with therespective polyethersulfone.

In some embodiments of the present invention, the additional (co)polymeris selected from one or more sulfonated (co)polymers. In the context ofthe present invention, the term “sulfonated (co)polymers” refers to(co)polymers that bear an average of at least one SO₃ ⁻-group permolecule of additional (co)polymer. In some cases, the sulfonated(co)polymer can bear an average of at least at least two SO₃ ⁻-groupsper molecule of additional (co)polymer. Said SO₃ ⁻-group (sulfonic acidgroups) may be free acid groups or salts, such as alkali metal salts orammonium salts or salts of organic amines including alkanol amines.

In one embodiment of the present invention, the additional (co)polymerhas a degree of sulfonation of up to 60%, or up to 55%. Generally, theterm “degree of sulfonation” refers to the number of sulfonic acidgroups per molecule of constitutional repeating unit.

In some instances, the sulfonated (co)polymers can include sulfonatedpolyketones, such as, for example, sulfonated polyether ketones andsulfonated polyether ether ketones (s PEEK).

Polyketones in the context of the present invention refer to(co)polymers that exhibit C═O-groups (keto groups) in theirconstitutional repeating units. Polyketones can be aliphatic,cycloaliphatic or aromatic. Examples include structural elements of theformula

with y being in the range of from 2 to 100, and v and w being selectedfrom 1 and 2.

Polyketones with v=w=1 are referred to as polyetherketone. In someembodiments, the polyetherketones can be obtained from polycondensationof 4-phenoxybenzoyl chloride and diphenyl ether.

Polyketones with v=2 and w=1 are referred to as polyether ether ketones(PEEK).

Polyketones with v=1 and w=2 are referred to as polyether ketone ketones(PEKK). In some embodiments, PEKK can be obtained from polycondensationof the dichloride of terephthalic acid with diphenyl ether.

Sulfonation of polyketones is known per se, see, e.g., US 2007/0117958and literature cited therein, which is incorporated herein by referencein its entirety for all purposes.

Other (co)polymers for use in the embodiments described herein areselected from polyethylene oxide (200K-8M), esters of polyethylene oxide(e.g., acetates, benzoates, and/or propionates), and/orpolyalkylvinylethers, e.g., poly-C₁-C₂₀-alkylvinylethers such aspolymethylvinylethers.

In one embodiment of the present invention, polyethersulfone has amolecular weight M_(w) of from about 25,000 to about 40,000 g/mol, fromabout 28,500 to about 35,000 g/mol, or from about 32,000 to about 34,000g/mol.

In one embodiment of the present invention, polyethersulfone iscross-linked with inorganic or organic filler. Cross-linking can beachieved, e.g., by irradiation such as UV/vis irradiation, byγ-irradiation, electron beams (e-beams) or by heating (thermalcross-linking). In the context of the present invention, the term“cross-linking” of polyethersulfone will not be limited to classicalcross-linking but will also include splitting of and recombining ofchains of polyethersulfone. Filler, as well as procedures and means forcross-linking, will be described in more detail below. In one embodimentof the present invention, polyethersulfone exhibits a polydispersityindex M_(w)/M_(n) of from about 3 to about 5, or from about 4 to about5.

Average molecular weight M_(n) and M_(w) can be determined byconventional means such as gel permetion chromatography (GPC).

Polyethersulfone can be incorporated in inventive electrochemical cellsin its gel state. When used in such a state, an auxiliary material suchas a solvent can be absorbed by the polyethersulfone. In someembodiments, the solvent can include at least one organic solvent. Insome embodiments, the solvent can comprise an aprotic organic solvent.Suitable organic solvents for converting polyethersulfone into its gelstate can be selected from organic amides such asN—C₁-C₁₀-alkylpyrrolidones, N—C₅-C₈-cycloalkylpyrrolidones, inparticular N-methylpyrrolidone, N-ethylpyrrolidone, andN-cyclohexylpyrrolidone. Further solvents are mentioned below.

According to one aspect of the present invention, the electrolyte of theinventive electrochemical cell comprises polyethersulfone (C) in its gelstate, the at least one organic solvent (D), at least one salt oflithium (E), optionally additional (co)polymer (F), and optionallyorganic or inorganic filler (G). Preferably the polyethersulfone istransformed into the gel state by incorporation of the at least one oforganic solvent (D) which contains at least one salt of lithium (E).

In one embodiment of the present invention, the electrolyte material(e.g., polyethersulfone or a blend of polyethersulfone and an additional(co)polymer) can be transformed into its gel state using mixtures ofsolvents, in particular mixtures comprising N—C₁-C₁₀-alkylpyrrolidonesand/or N—C₅-C₈-cycloalkylpyrrolidones.

In one embodiment of the present invention, the electrolyte (which caninclude polyethersulfone or a blend of polyethersulfone and additional(co)polymer(s), polyvinylalcohol (PVOH) or a blend of PVOH andadditional (co)polymer(s) or branched polyimide (HPI)) contains fromabout 1% to about 20% solvent, by weight, or from about 10% to about 15%solvent, by weight.

In one embodiment of the present invention, the electrolyte is arrangedin one or more layers with a thickness in the range of from about 1 nmto about 50 μm, from about 5 μm to about 15 μm, or from about 7 μm toabout 12 μm.

The electrolyte can have one or more mechanical properties that canimprove device performance during operation of the electrochemical cell.In some embodiments, the electrolyte can have a yield strength greaterthan the yield strength of lithium metal. In some cases, the electrolytematerial does not include an auxiliary material such as a solvent, inwhich case the yield strength of the non-fluid material in theelectrolyte (e.g., one or more polyethersulfones, one or more branchedpolyimide, polyvinylalcohol (PVOH) or a blend of PVOH and additional(co)polymer(s) and, optionally, other non-fluid materials such asadditional (co)polymer(s) and/or filler(s)) positioned between the anodeand the cathode can be greater than the yield strength of lithium metal.In instances where the electrolyte comprises an auxiliary material suchas a solvent, the yield strength of the combination of the non-fluidmaterial and the auxiliary material positioned between the anode and thecathode can be greater than the yield strength of lithium metal. Itshould be understood that the yield strength of any optional separatoris not included in the determination of the yield strength of theelectrolyte. In some embodiments, the electrolyte (e.g., the non-fluidmaterial, alone or in combination with an absorbed auxiliary material,for example, in the configurations described in the precedingparagraph), has a yield strength of at least about 80 Newtons/cm², atleast about 100 Newtons/cm², or at least about 120 Newtons/cm². In otherembodiments, the yield strength of the electrolyte (e.g., the non-fluidmaterial, alone or in combination with an absorbed auxiliary material,for example, in the configurations described in the precedingparagraph), may be at least 10% higher than the yield strength oflithium metal, at least 20% higher, at least 50% higher, at least 100%higher, or at least 200% higher than the yield strength of lithium.

The yield strength is the stress at which a material exhibits aspecified permanent deformation (sometimes referred to as plasticdeformation) and is a practical approximation of the elastic limit.Beyond the elastic limit, permanent deformation will occur. The loweststress at which permanent deformation during extension can be measuredis defined as yield stress according to the present invention. One ofordinary skill in the art would be capable of determining the yieldstrength of a material by, for example, taking a sample with a fixedcross-section area, and pulling it with a controlled, graduallyincreasing force until the sample changes shape or breaks. Longitudinaland/or transverse strain is recorded using mechanical or opticalextensometers. Testing machines for determing the yield strength arecommercially available, e.g. from Instron®.

The yield stress Y is correlated with the hardness value H for a pyramidindenter producing plastic flow. In many cases, the hardness Hcorrelates with the yield stress Y, with the hardness H corresponding toapproximately three times the yield stress Y (“Concise Encyclopedia ofpolymer science and engineering”, J. Kroschwitz editor 1990 John Wiley &Sons, page 441). Hardness, or resistance to local deformation, generallyrefers to the ease with which a material can be indented, drilled,sawed, or abraded. It generally involves a complex combination ofproperties, including yield strength, elastic modulus, andstrain-hardening capacity. Typically hardness is measured by staticpenetration of the material with a standard indenter exerting a knownforce, by dynamic rebound of a standard indenter of known mass droppedfrom a standard height, or by scratching with a standard pointed toolexerting a known force. One of ordinary skill in the art can apply thesemeasurements for gel-polymer films and metallic lithium and comparetheir relative hardness and/or yield strength.

In some instances, the electrolyte (e.g., the non-fluid material, aloneor in combination with an absorbed auxiliary material, for example, inthe configurations described in the preceding paragraph) has a thicknessof at least about 5 μm, at least about 10 μm, at least about 25 μm,between about 1 μm and about 500 μm between about 5 μm and about 100 μm,or between about 5 microns and about 20 microns.

In some embodiments, the electrolyte, when configured for use in anelectrochemical cell, can have a yield strength and/or thickness withinany of the ranges outlined above. Generally, an electrolyte isconfigured for use in an electrochemical cell when it includes allmaterials that would be within the boundaries of the electrolyte (e.g.,non-fluid material (e.g., solid material), auxiliary material such as asolvent), is packaged as it would be during use, and is under conditionsit would be exposed to (e.g., temperature, pressure, etc.) during use.Generally, the electrochemical cells described herein that areconfigured for use are capable of exhibiting the ionic conductivitiesand electrical conductivities necessary to charge and discharge the cellat the desired level. As a specific example, in some cases, theelectrolyte can comprise a gel comprising a non-fluid material (e.g.,comprising one or more polyethersulfone, one or more branched polyimide,polyvinylalcohol or a blend of PVOH and additional (co)polymer(s)) andan auxiliary material. The electrolyte gel can be positioned between theanode and the cathode such that the non-fluid material has a surface incontact with a surface of the anode. In some cases, a second surface ofthe electrolyte gel can be in contact with the cathode, or in contactwith a separator between the electrolyte gel and the cathode. In someembodiments, the electrolyte gel, when configured for use, can have ayield strength greater than the yield strength of lithium metal (e.g.,at least about 80 Newtons/cm², at least about 100 Newtons/cm², or atleast about 120 Newtons/cm²). The yield strength of the electrolyte gel,when configured for use may be at least 10% higher than the yieldstrength of lithium metal, at least 20% higher, at least 50% higher, atleast 100% higher, or at least 200% higher than the yield strength oflithium. In some instances, the electrolyte gel can have a thickness ofat least about 5 μm, at least about 10 μm, at least about 25 μm, betweenabout 1 μm and about 500 μm between about 5 μm and about 100 μm, orbetween about 5 μm and about 20 μm.

Examples of polymer electrolyte gels having a yield strength higher thanlithium include, for example, materials (e.g., films) based onnon-porous polyvinylalcohol (PVOH) as a non-fluid material swollen witha solvent having affinity to PVOH such as, for example,dimethylacetamide (DMAc), N-methylpyrolidone (NMP), dimethylsulfoxide(DMSO), dimethylformamide (DMF), sulfolanes and sulfones. The PVOH maybe swollen in solvent mixture comprising a solvent having affinitiy toPVOH and also solvents having no affinity to PVOH (so-callednon-solvents) like 1,2.dimethoxyethane (DME), diglyme, triglyme,1,3-dioxolane (DOL), THF, 1,4-dioxane, cyclic and linear ethers, esters(carbonates as dimethylcarbonate and ethylene carbonate), acetals andketals. The solvent or solvent mixture may contain one or more lithiumsalts such as, for example, (CF₃SO₂)₂NLi (LiTFSI), CF₃SO₃Li, LiNO₃,LiBOB, LiPF₆, LiSCN, LiClO₄, LiI, LiBr, LiCl, LiBF₄ and further lithiumsalts mentioned elsewhere herein.

The polymer electrolyte gel comprising non-porous PVOH may be preparedby exposing the PVOH to the solvent/solvent mixture and swelling withthe solvent/solvent mixture to an equilibrium concentration. Forexample, the solvent mixture for preparing the polymer electrolyte gelcan comprise a mixture of a solvent like DMAc, NMP or

DMSO with non-solvents like DME and DOL. The concentration of DMAc (NMP,DMSO) in the solvent mixture can be from 5 to 80 w %. Solvent uptake inthe swollen PVOH can be in the range from 5 to 50 weight %. Forinstance, experiments have shown that PVOH exposed to mixture of 40 w %DMAc and 60 w % of Dioxane can uptake 19% of DMAc. Also PVOH can beswollen first with solvent and then exposed to the mixture of solvent,optionally non-solvent and electrolyte salt (e.g., lithium salt), insome embodiments. In some embodiments, PVOH can be coated as a film froma solution comprising a solvent, salt and other solvents, and dried toreduce solvent content in the gel-polymer to the desired level.Non-porous PVOH refers to a continuous polymer film/material based onPVOH substantially free of defects or porosity.

Other examples of polymer electrolyte gels having a yield strengthhigher than lithium are composites of non-porous PVOH and/or copolymersof PVOH with further (co) polymer(s) wherein the PVOH and/or copolymerof PVOH (and/or the further (co) polymer(s)) form a interpenetratingnetwork wherein the PVOH/copolymer of PVOH is not swollen and thefurther (co) polymer(s) are swollen by a solvent or solvent mixturecomprining solvents having affinity to the further (co) polymer(s) buthaving no or only low affinity to PVOH. Examples for the further (co)polymer(s) are polysulfones, polyethersulfones, polyethyleneoxides,polypropyleneoxides, polystyrene, polyvinylidene fluoride and polyalkylvinyl ethers. The solvent/solvent mixtures used for swelling the further(co)polymers may comprise one or more lithium salts as described below.

According to another embodiment of the present invention, the non-fluidmaterial may be selected from porous PVOH wherein the pores are filledwith one or more non-solvents for PVOH. Examples for non-solvents forPVOH are mentioned above. The non-solvents may contain electrolytesalts, including those selected from the lithium salts mentioned below.Films of porous PVOH can be made through various techniques including,for example, coating with dispersed removable filler, phase separationwith solvent/non-solvent precipitation, and slurry coating withdispersed inorganic fillers listed below. PVOH porous films exposed tonon-solvents for PVOH do not generally form a gel. Porous PVOH refers toa continuous polymer film/material which has holes or pores. Porous PVOHcan be determined by a test such as a solvent uptake (e.g., DBP uptake)test, a gas permeability test, or a mercury intrusion test.

Polymer electrolyte gels having yield strength higher than lithium mayfurther be prepared from branched and hyperbranched polyimides.Hyperbranched polyimides are a subclass of branched polyimides. They arecomposed of highly branched macromolecules in which any linear subchainmay lead in either direction to at least two other subchains. Herein,the term “branched polyimides” is intended to include branched andhyperbranched polyimides. The branched polyimides are, in someembodiments, selected from condensation products of

-   -   (a) at least one polycarboxylic acid having at least 3 COOH        groups per molecule or anhydride or ester thereof, and    -   (b) at least one compound, selected from        -   (b1) at least one polyamine having on average more than two            amino groups per molecule, and in some cases, also referred            to as polyamine (b1), and in some cases from        -   (b2) at least one polyisocyanate having on average more than            two isocyanate groups per molecule, also referred to as            polyisocyanate (b2).

Said polyimide is briefly referred to as a branched polyimide.

The branched polyimide can have a molecular weight M_(w) in the rangefrom 1,000 to 200,000 g/mol. In some embodiments, the branched polyimidecan have a molecular weight M_(w) in the range from 2,000 to 20,000g/mol.

The branched polyimide can have at least two imide groups per molecule.In some embodiments, the branched polyimide can have at least 3 imidegroups per molecule.

In one embodiment, the branched polyimide can have up to 1,000 imidegroups per molecule. In some embodiments, the branched polyimide canhave up to 660 per molecule.

In one embodiment, the recitation of the number of isocyanate groups orthe number of COOH groups per molecule in each case denotes the meanvalue (number-average).

The branched polyimide can be composed of structurally and molecularlyuniform molecules. In some embodiments, the branched polyimides comprisemixtures of molecularly and structurally differing molecules, forexample, visible from the polydispersity M_(w)/M_(n) of at least 1.4,and, in some cases, M_(w)/M_(n) of 1.4 to 50, or 1.5 to 10. Thepolydispersity can be determined by known methods, in particular by gelpermeation chromatography (GPC). A suitable standard is, for example,poly(methyl methacrylate) (PMMA).

In one embodiment, polyimide (B), in addition to imide groups which formthe polymer backbone, comprises, terminally or in side chains, inaddition at least three, at least six, or at least ten, terminal orside-chain functional groups. The functional groups in the branchedpolyimide can comprise anhydride and/or acid groups and/or free orcapped NCO groups. In some embodiments, the branched polyimides have nomore than 500 terminal or side-chain functional groups, or no more than100 terminal or side-chain functional groups.

Alkyl groups such as, for example, methyl groups are therefore not abranching of a molecule of branched polyimide.

In some embodiments, polycarboxylic acids (a) include aliphatic, or insome embodiments aromatic. In some embodiments, polycarboxylic acids areselected that have at least three COOH groups per molecule, or therespective anhydrides, for example if they are present in low-molecularweight, that is to say, non-polymeric form. Polycarboxylic acids havingthree COOH groups in which two carboxylic acids groups are present asanhydride and the third as a free carboxylic acid can also be used.

In one embodiment, polycarboxylic acid (a) comprises a polycarboxylicacid having at least 4 COOH groups per molecule, or the respectiveanhydride.

Examples of polycarboxylic acids (a) and anhydrides thereof are1,2,3-benzenetricarboxylic acid and 1,2,3-benzenetricarboxylicdianhydride, 1,3,5-benzenetricarboxylic acid (trimesic acid), including1,2,4-benzenetricarboxylic acid (trimellitic acid), trimelliticanhydride and, in particular, 1,2,4,5-benzenetetracarboxylic acid(pyromellitic acid) and 1,2,4,5-benzenetetracarboxylic dianhydride(pyromellitic dianhydride), 3,3′,4,4″-benzophenonetetracarboxylic acid,3,3′,4,4″-benzophenonetetracarboxylic dianhydride, in additionbenzenehexacarboxylic acid (mellitic acid) and anhydrides of melliticacid.

Other suitable polycarboxylic acids (a) and anhydrides thereof aremellophanic acid and mellophanic anhydride,1,2,3,4-benzenetetracarboxylic acid and 1,2,3,4-benzenetetracarboxylicdianhydride, 3,3,4,4-biphenyltetracarboxylic acid and3,3,4,4-biphenyltetracarboxylic dianhydride,2,2,3,3-biphenyltetracarboxylic acid and 2,2,3,3-biphenyltetracarboxylicdianhydride, 1,4,5,8-naphthalenetetracarboxylic acid and1,4,5,8-naphthalenetetracarboxylic dianhydride,1,2,4,5-naphthalenetetracarboxylic acid and1,2,4,5-naphthalenetetracarboxylic dianhydride,2,3,6,7-naphthalenetetracarboxylic acid and2,3,6,7-naphthalenetetracarboxylic dianhydride,1,4,5,8-decahydronaphthalenetetracarboxylic acid and1,4,5,8-decahydronaphthalenetetracarboxylic dianhydride,4,8-dimethyl-1,2,3,5,6,7-hexahydronaphthalene-1,2,5,6-tetracarboxylicacid and4,8-dimethyl-1,2,3,5,6,7-hexahydronaphthalene-1,2,5,6-tetracarboxylicdianhydride, 2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic acid and2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride,2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic acid and2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride,2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic acid and2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic dianhydride,1,3,9,10-phenanthrenetetracarboxylic acid and1,3,9,10-phenanthrenetetracarboxylic dianhydride,3,4,9,10-perylenetetracarboxylic acid and3,4,9,10-perylenetetracarboxylic dianhydride,bis(2,3-dicarboxyphenyl)methane and bis(2,3-dicarboxyphenyl)methanedianhydride, bis(3,4-dicarboxyphenyl)methane andbis(3,4-dicarboxyphenyl)methane dianhydride,1,1-bis(2,3-dicarboxyphenyl)ethane and1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride,1,1-bis(3,4-dicarboxyphenyl)ethane and1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride,2,2-bis(2,3-dicarboxyphenyl)propane and2,2-bis(2,3-dicarboxyphenyl)propane dianhydride,2,3-bis(3,4-dicarboxyphenyl)propane and2,3-bis(3,4-dicarboxyphenyl)propane dianhydride,bis(3,4-carboxyphenyl)sulfone and bis(3,4-carboxyphenyl)sulfonedianhydride, bis(3,4-carboxyphenyl) ether and bis(3,4-carboxyphenyl)ether dianhydride, ethylenetetracarboxylic acid andethylenetetracarboxylic dianhydride, 1,2,3,4-butanetetracarboxylic acidand 1,2,3,4-butanetetracarboxylic dianhydride,1,2,3,4-cyclopentanetetracarboxylic acid and1,2,3,4,-cyclopentanetetracarboxylic dianhydride,2,3,4,5-pyrrolidinetetracarboxylic acid and2,3,4,5-pyrrolidinetetracarboxylic dianhydride,2,3,5,6-pyrazinetetracarboxylic acid and 2,3,5,6-pyrazinetetracarboxylicdianhydride, 2,3,4,5-thiophenetetracarboxylic acid and2,3,4,5-thiophenetetracarboxylic dianhydride.

In one embodiment, anhydrides from U.S. Pat. No. 2,155,687 or U.S. Pat.No. 3,277,117 are used for synthesizing a branched polyimide.

Polycarboxylic acid (a) or its respective anhydride can be reacted withat least one compound (b), selected from

-   -   (b1) at least one polyamine having on average more than two        amino groups per molecule, also referred to as polyamine (b1),        and in some cases,    -   (b2) at least one polyisocyanate having on average more than two        isocyanate groups per molecule, also referred to as        polyisocyanate (b2).

In some embodiments, polycarboxylic acid (a) or its respective anhydridewill be reacted

-   -   either with at least one polyamine (b1)    -   or, in some cases, with at least one polyisocyanate (b2).

Polyamines (b1) can be aliphatic, cycloaliphatic, or, in someembodiments, aromatic. Generally, in polyamine (b1) only primary aminogroups (NH₂-groups) will be taken into account. Tertiary and secondaryamino groups—if present—will not be taken into consideration whendetermining the number of amino groups in polyamine (b1).

In some embodiments, polyamine (b1) has on average more than two aminogroups per molecule, on average at least 2.5 amino groups per molecule,or on average at least 3.0 amino groups per molecule.

In one embodiment, polyamines (b1) are selected from mixtures fromdiamines and triamines.

In one embodiment, polyamine (b1) bears on average a maximum of 8. Insome embodiments, polyamine (b1) bears on average a maximum of 6 aminegroups per molecule.

In some embodiments, aromatic triamines and mixtures of aromatic oraliphatic diamines and aromatic triamines can be used for polyamines(b1).

Examples for aliphatic diamines to be present in said mixtures ofmixtures of aromatic or aliphatic diamines and aromatic triamines aspolyamines (b1) are ethylene diamine, 1,3-propylene diamine,diethylenetriamine, tetraethylenepentamine, and triethylenetetramine.

Suitable aromatic triamines that can be selected as polyamines(b1)—alone or as a mixture with at least one aromatic diamine—are chosenfrom triamines in which the NH₂ groups are attached to one (or in somecases to at least two) aromatic rings, said different aromatic ringsbeing so-called isolated aromatic rings, conjugated aromatic rings, orfused aromatic rings.

In some embodiments, triamines with NH₂-groups attached to differentconjugated or isolated aromatic rings are selected. Examples are1,3,5-tri(4-aminophenoxy) benzene, 1,3,5-tri(3-methy 1,4-aminophenoxy)benzene, 1,3,5-tri(3-methoxy, 4-aminophenoxy) benzene,1,3,5-tri(2-methyl, 4-aminophenoxy) benzene, 1,3,5-tri(2-methoxy,4-aminophenoxy) benzene, and 1,3,5-tri(3-ethyl, 4-aminophenoxy)benzene.

Further examples for triamines are 1,3,5-tri(4-aminophenylamino)benzene, 1,3,5-tri(3-methyl, 4-aminophenylamino) benzene,1,3,5-tri(3-methoxy, 4-aminophenylamino) benzene, 1,3,5-tri(2-methyl,4-aminophenylamino) benzene, 1,3,5-tri(2-methoxy,4-aminophenylamino)benzene, and 1,3,5-tri(3-ethyl,4-aminophenylamino) benzene.

Examples are triamines according to formula (VII)

the integers being defined as follows:

R⁵, R⁶—being different or identical and selected from hydrogen,C₁-C₄-alkyl, COOCH₃, COOC₂H₅, CN, CF3, or O—CH₃;

X¹, X²—being different or identical and selected from single bonds,C₁-C₄-alkylene groups, N—H, and oxygen, or —CH₂— or oxygen.

In one embodiment, polyamine (b1) is selected from3,5-di(4-aminophenoxy)aniline, 3,5-di(3-methyl-1,4-aminophenoxy)aniline,3,5-di(3-methoxy-4-aminophenoxy)aniline,3,5-di(2-methyl-4-aminophenoxy)aniline,3,5-di(2-methoxy-4-aminophenoxy)aniline, and3,5-di(3-ethyl-4-aminophenoxy)aniline.

In one embodiment, examples are triamines according to formula (VIII)

R⁷ selected from hydrogen, C₁-C₄-alkyl, COOCH₃, COOC₂H₅, CN, CF₃, orO—CH₃;

R⁸ selected from hydrogen or methyl

and the other integers being defined as above.

Polyisocyanate (b2) can be selected from any polyisocyanates that onaverage have more than two isocyanate groups per molecule, which can becapped or free. In some embodiments, trimeric or oligomericdiisocyanates can be used, for example oligomeric hexamethylenediisocyanate, oligomeric isophorone diisocyanate, oligomeric tolylenediisocyanate, including trimeric tolylene diisocyanate, oligomericdiphenylmethane diisocyanate—hereinafter also termed polymer-MDI—andmixtures of the abovementioned polyisocyanates. For example, what istermed trimeric hexamethylene diisocyanate, in many cases, is notpresent as pure trimeric diisocyanate, but as polyisocyanate having amedium functionality of 3.6 to 4 NCO groups per molecule. The sameapplies to oligomeric tetramethylene diisocyanate and oligomericisophorone diisocyanate.

In one embodiment, polyisocyanate (b2) having more than two isocyanategroups per molecule is a mixture of at least one diisocyanate and atleast one triisocyanate, or a polyisocyanate having at least 4isocyanate groups per molecule.

In one embodiment, polyisocyanate (b2) has on average at least 2.2, atleast on average 2.5, or at least on average 3.0, isocyanate groups permolecule.

In one embodiment, polyisocyanate (b2) bears on average a maximum of 8,or on average a maximum of 6 isocyanate groups per molecule.

In one embodiment, polyisocyanate (b2) is selected from oligomerichexamethylene diisocyanate, oligomeric isophorone diisocyanate,oligomeric diphenylmethane diisocyanate, and mixtures of theabovementioned polyisocyanates.

Polyisocyanate (b2) can, in addition to urethane groups, also have oneor more other functional groups, for example urea, allophanate, biuret,carbodiimide, amide, ester, ether, uretonimine, uretdione, isocyanurateor oxazolidine groups.

When polyamine (b1) and polycarboxylic acid (a) are condensed with oneanother—in some embodiments, in the presence of a catalyst—an imidegroup is formed under elimination of H₂O.

In the above formulae, R* is the polyamine (b1) radical that is notspecified further in the above reaction equation, and n is a numbergreater than or equal to 1, for example 1 in the case of a tricarboxylicacid or 2 in the case of a tetracarboxylic acid. Optionally, (HOOC)_(n)can be replaced with a C(═O)—O—C(═O) moiety.

In some embodiments, when polyisocyanate (b2) and polycarboxylic acid(a) are condensed with one another—in some embodiments, in the presenceof a catalyst—an imide group is formed with the elimination of CO₂ andH₂O. If, instead of polycarboxylic acid (a), the corresponding anhydrideis used, an imide group can be formed with elimination of CO₂.

In the above formulae, R** is the polyisocyanate (b2) radical that isnot specified further in the above reaction equation, and n is a numbergreater than or equal to 1, for example in the case of a tricarboxylicacid or in the case of a tetracarboxylic acid, and optionally,(HOOC)_(n) can be replaced with a C(═O)—O—C(═O) moiety.

In some embodiments, polyisocyanate (b2) is used in a mixture with atleast one diisocyanate, for example with tolylene diisocyanate,hexamethylene diisocyanate or with isophorone diisocyanate. In aparticular variant, polyisocyanate (b2) is used in a mixture with thecorresponding diisocyanate, for example trimeric HDI with hexamethylenediisocyanate or trimeric isophorone diisocyanate with isophoronediisocyanate or polymeric diphenylmethane diisocyanate (polymer MDI)with diphenylmethane diisocyanate.

In some embodiments, polycarboxylic acid (a) is used in a mixture withat least one dicarboxylic acid or with at least one dicarboxylicanhydride, for example with phthalic acid or phthalic anhydride.

Exemplary synthesis methods for making branched polyimides are describedbelow.

In some embodiments, synthesis methods for making branched polyimidescomprise reacting with one another:

-   -   (a) at least one polycarboxylic acid having at least 3 COOH        groups per molecule or anhydride or ester thereof, and    -   (b) at least one compound, selected from        -   (b1) at least one polyamine having on average more than two            amino groups per molecule and        -   (b2) at least one polyisocyanate having on average more than            two isocyanate groups per molecule

in the presence of a catalyst.

In some embodiments, water and Brønsted bases are suitable for use ascatalysts, for example alkalimetal alcoholates (e.g., alkanolates ofsodium or potassium, for example sodium methanolate, sodium ethanolate,sodium phenolate, potassium methanolate, potassium ethanolate, potassiumphenolate, lithium methanolate, lithium ethanolate and lithiumphenolate).

For carrying out the synthesis method for making branched polyimides,polyisocyanate (b2) and polycarboxylic acid (a) or anhydride (a) can beused in a quantitative ratio such that the molar fraction of NCO groupsto COOH groups is in the range from 1:3 to 3:1, or from 1:2 to 2:1. Inthis case, one anhydride group of the formula CO—O—CO counts as two COOHgroups.

In some embodiments, catalyst can be used in the range from 0.005 to0.1% by weight, based on the sum of polyisocyanate (b2) andpolycarboxylic acid (a) or polyisocyanate (b2) and anhydride (a). Insome embodiments, the catalyst the percentage of the catalyst can bebetween 0.01 to 0.05% by weight.

In some embodiments, a synthesis method for making branched polyimidescan be carried out at temperatures in the range from 50 to 200° C., from50 to 140° C., or from 50 to 100° C.

In some embodiments, a synthesis method for making branched polyimidescan be carried out at atmospheric pressure. However, the synthesis isalso possible under pressure, for example at pressures in the range from1.1 to 10 bar.

In some embodiments, a synthesis method for making branched polyimidescan be carried out in the presence of a solvent or solvent mixture.Examples of suitable solvents are N-methylpyrrolidone,N-ethylpyrrolidone, dimethylformamide, dimethylacetamide, dimethylsulfoxide, dimethyl sulphones, xylene, phenol, cresol, ketones such as,for example, acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone(MIBK), acetophenone, in addition mono- and dichlorobenzene, ethyleneglycol monoethyl ether acetate and mixtures of two or more of theabovementioned mixtures. In this case, the solvent or solvents can bepresent during the entire synthesis time or only during part of thesynthesis.

The reaction can be carried out, for example, for a time period of 10minutes to 24 hours.

In some embodiments, the synthesis method for making branched polyimidesis carried out under inert gas, for example under argon or undernitrogen.

If a water-sensitive Brønsted base is used as a catalyst, a dry inertgas and solvent can be used. If water is used as catalyst, the drying ofsolvent and inert gas can be dispensed with.

In a variant of the synthesis method for making branched polyimides, NCOend groups of branched polyimide can be blocked with a blocking agent(c), for example with secondary amine, for example with dimethylamine,di-n-butylamine or with diethylamine.

The solvents for preparing the polymer gel based on branched polyimidemay be selected from the solvents described below and may compriseelectrolyte salts, including lithium salts selected from the lithiumsalts described below.

As another specific example, in some cases, the non-fluid material ofthe electrolyte itself serves as a solid electrolyte. The non-fluidmaterial in this set of embodiments may be used in the substantialabsence of an auxiliary material (e.g., a solvent) during use, in whichcase, the yield strength is measured in the absence of auxiliarymaterials. In other cases, the solid electrolyte might be used inconjunction with an auxiliary material (e.g., a solvent) during use, inwhich case, the yield strength of the electrolyte would be measured asthe yield strength of the combination of the solid electrolyte and theauxiliary material. In either case, the electrolyte, when configured foruse, can have a yield strength within any of the ranges described aboveand/or a thickness within any of the ranges described above.

In one embodiment of the present invention, the electrolyte (e.g.,electrolyte gel) can exhibit an ionic conductivity of at least about5×10⁻⁶ S/cm, at least about 5×10⁻⁵ S/cm, at least about 5×10⁻⁴ S/cm,from about 10⁻⁶ to about 10⁻³ S/cm, or from about 10⁻⁵ to about 10⁻²S/cm in the gel state at room temperature. One of ordinary skill in theart would be capable of determining the ionic conductivity of theelectrolyte using impedance spectroscopy.

The electrolyte material can be placed between the cathode and the anodein a variety of configurations. For example, in some embodiments, theelectrolyte material can be placed between the anode and an optionalseparator, which is discussed in more detail below. In some instances,the electrolyte material can be positioned between the anode and thecathode such that the electrolyte material has a surface in contact witha surface of the anode (e.g., anode active surface 20 in FIG. 1 ). Forexample, in some cases, the electrolyte can be formed as a layer overthe anode, in which case, the electrolyte and the anode can beintegrated with (e.g., covalently bonded to) each other. In one set ofembodiments, the electrolyte material can serve as a separator, and noadditional separator is required.

As mentioned above, the electrolyte can include an auxiliary material insome cases. The auxiliary material can be a fluid (e.g., a liquid) insome embodiments. For example, the electrolyte can include a fluidauxiliary material absorbed within a non-fluid material (e.g., as in thecase of a polyethersulfone gel, a branched polyimide gel, a gel based onpolyvinylalcohol or the composite of PVOH and additional (co)polymer(s)described above, or the porous PVOH comprising a non-solvent for PVOH).In some embodiments, the auxiliary material within the electrolyte canbe an electrolyte solvent.

Exemplary suitable solvents for use in the electrochemical cellsdescribed herein include organic solvents. In some embodiments, theorganic solvents have no active hydrogen but are sufficiently polar todissolve a salt. Exemplary organic solvents can be selected fromdioxolanes, dioxanes, organic carbonates, cyclic ethers and non-cyclicethers.

Organic solvents can be selected from non-cyclic ethers includingdiethers, polyethers and cyclic ethers, acetals, and particularlyorganic carbonates. Among polyethers, polyethers that are liquid artroom temperature can be preferred, in some cases.

Examples for suitable non-cyclic ethers, diethers, and polyethers arediisopropylether, di-n-butylether, 1,2-dimethoxyethane,1,2-diethoxyethan, diglyme (diethylene glycol dimethyl ether), triglyme(triethylenglycol dimethyl ether).

Examples for suitable cyclic ethers are tetrahydrofurane and1,4-dioxane.

Acetals can be cyclic or non-cyclic. Examples for suitable non-cyclicacetals are dimethoxymethane, diethoxymethane, 1,1-dimethoxyethane and1,1-diethoxyethane. Examples for suitable cyclic acetals are 1,3-dioxaneand in particular 1,3-dioxolane.

Examples for suitable organic carbonates are compounds according to thegeneral formula (II) or (III)

R⁵, R⁶ and R⁷ being different or equal and being selected from hydrogenand C₁-C₄-alkyl, e.g. methyl, ethyl, n-propyl, iso-propyl, n-butyl,iso-butyl, sec.-butyl and tert.-butyl. In some cases, R⁶ and R⁷ are notboth tert.-Butyl.

In one set of embodiments of the present invention, R⁵ is selected frommethyl, and R⁶ and R⁷ are both hydrogen, or R⁵, R⁶ and R⁷ are eachhydrogen.

Inventive electrochemical cells further comprise at least one salt. Saltcan be selected from salts of lithium or sodium. In particular, if thecathode contains lithium, salt can be selected from lithium salts.

Suitable lithium salts are selected from lithium nitrate, LiPF₆, LiBF₄,LiClO₄, LiAsF₆, LiCF₃SO₃, LiC(C_(n)F_(2n+1)SO₂)₃, lithium imides such asLiN(C_(n)F_(2n+1)SO₂)₂, wherein n is an integer in the range of from 1to 20, or LiN(SO₂F)₂, lithium bis-oxalatoborate (LiBOB), furthermoreLi₂SiF₆, LiSbF₆, LiAlCl₄, and salts of the general formula(C_(n)F_(2n+1)SO₂)_(m)XLi with m being 1 when X is selected from oxygenor sulfur, m being 2 when X is selected from nitrogen or phosphorus, andm being 3 when X is selected from carbon or silicium and n is an integerin the range of from 1 to 20. Suitable salts are selected fromLiC(CF₃SO₂)₃, LiN(CF₃SO₂)₂, LiN(SO₂F)₂, LiPF₆, LiBF₄, LiClO₄, andLiCF₃SO₃.

The concentration of salt in solvent can be in the range of from about0.5 to about 2.0 M, from about 0.7 to about 1.5 M, or from about 0.8 toabout 1.2 M (wherein M signifies molarity, or moles per liter).

In one embodiment of the present invention, solution of salt insolvent(s) can comprise at least one further ingredient such as lithiumnitrate, lithium bis-(trifluoromethylsulfon)imide, guanidinium nitrate,and/or g pyridinium nitrate.

In one embodiment of the present invention, inventive electrochemicalcells comprise at least one filler. The filler can be selected fromorganic and inorganic fillers or combinations thereof. Fillers in thecontext of the present invention are selected from solid materials thatare insoluble in the electrolyte.

Suitable inorganic fillers may be selected from metal oxides, metalnitrides, metals, and organic polymers. Examples of fillers are Al₂O₃,AlOOH, TiO₂, SiO₂, silica (hydrophobic or hydrophilic, including, forexample fumed silica and silica fibres), clay, aluminium Boehmite,silicates (e.g., alumosilicates), and nitrides such as AN, BN, and Li₃N.

Suitable organic fillers may be selected from organic polymers such ascellulose (e.g., cellulose fibres or cellulose powder) or starch.

Filler can have a crystalline or an amorphous structure. Any of thepolymers used herein can be crystalline, partially crystalline oramorphous.

In some embodiments, one or more fillers can be part of the non-fluidmaterial within the electrolyte. For example, in some cases, one or morefillers can be mixed with one or more polyethersulfones and/or a blendof polyethersulfone and one or more additional (co)polymer(s), branchedpolyimide, PVOH or a blend of PVOH and further (co)polymers. In oneembodiment of the present invention, the electrolyte can contain fromabout 1% to about 95% filler, by weight, or from about 5% to about 90%filler, by weight.

In one embodiment of the present invention, filler is in the form ofparticles or powder whose smallest aspect dimension is up to about 50%of the thickness of the layer of polyethersulfone or of the layer ofblend of polyethersulfone and additional (co)polymer. In this context,an aspect dimension is selected from diameter, length, breadth andheight.

In a particular embodiment of the present invention, the filler and oneor more components of the non-fluid material in the electrolyte (e.g.,polyethersulfone, branched polyimide or PVOH) are covalently linked toeach other, thus forming a compound. Covalent linkage between the fillerand non-fluid material in the electrolyte can be achieved, e.g., byadding cross-linker to the non-fluid material and the filler andperforming a cross-linking reaction, e.g. by thermal or photochemicalcuring.

Suitable cross-linkers are selected from molecules with two or morecarbon-carbon double bonds, especially with two or more vinyl groups.Particularly useful cross-linkers are selected from di(meth)acrylates ofdiols such as glycol, propylene glycol, diethylene glycol, dipropyleneglycol, 1,3-propanediol, 1,4-butanediol, triethylene glycol,tetrapropylene glycol, or the like. Further particularly suitablecross-linkers are selected from cyclopentadiene dimer, 1,3-divinylbenzene, and 1,4-divinyl benzene. Some suitable cross-linkers cancomprise two or more epoxy groups in the molecule, such as, for example,bis-phenol F, bis-phenol A, 1,4-butanediol diglycidyl ether, glycerolpropoxylate triglycidyl ether, and the like.

In one embodiment of the present invention, the organic polymer used asnon-fluid material, e.g. polyethersulfone, polyimide, and/or PVOHoptionally together with an additional (co)polymer is cross-linked.Cross-linking can be achieved, e.g., by adding cross-linker to thepolysulfone and performing a cross-linking reaction, e.g. by thermal orphotochemical curing, e.g. by irradiation with such as UV/visirradiation, by γ-irradiation, electron beams (e-beams) or by heating(thermal cross-linking). The term “cross-linking” of polyethersulfone isnot limited to classical cross-linking but also includes splitting ofand recombining of chains of polyethersulfone. Suitable cross-linkersare the cross-linkers for cross-linking filler and non-fluid material inthe electrolyte, e.g, polyethersulfone described above.

Referring back to FIG. 1 , in one embodiment of the present invention,inventive electrochemical cells further contain an optional separator22. The optional separator can serve to mechanically separate thecathode and the anode to prevent short-circuiting between the anode andthe cathode, while allowing ions and solvent to be exchanged between theanode and the cathode. The separator can comprise synthetic ornon-synthetic organic polymeric materials, and can be selected frompolymer/ceramic material hybrid systems such as polymer non-wovenmaterials coated with a ceramic material. Suitable materials for theseparator are polyolefins (e.g., polyethylene or polypropylene) andfluorinated (co)polymers. The separator can comprise a microporous film,in some cases.

As mentioned above, a separator 22 independent of electrolyte 16 is anoptional feature, and in one set of embodiments, the electrolytematerial can serve as the separator.

Fluorinated (co)polymers in the context of the present invention referto (co)polymers in which at least one (co)monomer bears at least onefluorine atom per molecule. Suitable fluorinated polymers include(co)polymers in which each (co)monomer bears at least one fluorine atomper molecule. In some cases, the fluorinated polymer can include(co)polymers in which each (co)monomer bears at least two fluorine atomsper molecule. Examples of suitable fluorinated (co)polymers includepolytetrafluoroethylene, tetrafluoroethylene hexafluoropropylenecopolymers, polyvinylidene fluoride, vinylidene fluoridehexafluoropropylene copolymers and vinylidene tetrafluoroethylenecopolymers.

In some embodiments, the separator can be a porous or microporousmaterial. The porous material can be characterized by, e.g., the porediameter and the porosity or by the Gurley method.

In one set of embodiments of the present invention, the average porediameter of separator can be from about 0.1 μm to about 50 μm, or fromabout 10 to about 30 μm.

In one set of embodiments of the present invention, the porosity ofseparator can be from about 30 to about 80%, or from about 40 to about70%.

In one embodiment of the present invention, the separator has apermeability for gas in the range of from about 50 to about 1,000 Gurleyseconds.

The cathode, anode, electrolyte, and/or—if present—separator can haveany suitable shape and/or size. In some embodiments, the cathode, anode,electrolyte, and/or optional separator are layers or films each with athickness in the range of from about 10 μm to about 1000 μm, or fromabout 100 μm to about 500 μm.

In one set of embodiments of the present invention, the cathode has athickness in the range of from about 1 μm to about 500 μm, or from about100 μm to about 200 μm.

In one set of embodiments of the present invention, the anode has athickness of from about 5 to about 50 μm, or from about 10 to about 20μm.

In one set of embodiments of the present invention, separator can have athickness of from about 5 μm to about 50 μm, or from about 7 to about 25μm.

In some embodiments, polyethersulfone (C) is placed between electrode(A) and electrode (B), between electrode (B) and separator (I) or on thesurface of electrode (B).

In some embodiments, electrode (B) is a multi-layer electrode comprisingfilm(s) of lithium or lithium alloy, polyether sulfone (C), optionallyadditional (co)polymer (F), and optionally organic or inorganic filler(G).

Inventive electrochemical cells can be advantageously used for makingbatteries, especially secondary batteries. Said batteries can have goodproperties such as high capacity per volume or kg, they can be rechargedwith little capacity loss in many cycles, and/or they do not exhibit thethermal runaway at elevated temperatures such as 150° C. to 230° C.

In some embodiments, the electrochemical cells described herein can becycled at relatively high temperatures without experiencing thermalrunaway. The term “thermal runaway” is understood by those of ordinaryskill in the art, and refers to a situation in which the electrochemicalcell cannot dissipate the heat generated during charge and dischargesufficiently fast to prevent uncontrolled temperature increases withinthe cell. Often, a positive feedback loop can be created during thermalrunaway (e.g., the electrochemical reaction produces heat, whichincreases the rate of the electrochemical reaction, which leads tofurther production of heat), which can cause electrochemical cells tocatch fire. In some embodiments, the electrolyte (e.g., the polymermaterial within the electrolyte) can be configured such that thermalrunaway is not observed at relatively high temperatures of operation ofthe electrochemical cell. Not wishing to be bound by any particulartheory, the polymer within the electrolyte (e.g., polyethersulfone) mayslow down the reaction between the lithium (e.g., metallic lithium) andthe cathode active material (e.g., sulphur such as elemental sulfur) inthe electrochemical cell, inhibiting (e.g., preventing) thermal runawayfrom taking place. Also, the polymer within the electrolyte may serve asa physical barrier between the lithium and the cathode active material,inhibiting (e.g., preventing) thermal runaway from taking place.

In some embodiments, the electrolyte (e.g., the polymer within theelectrolyte) can be configured such that the electrochemical cell can beoperated (e.g., continuously charged and discharged) at a temperature ofup to about 130° C., up to about 150° C., up to about 170° C., up toabout 190° C., up to 210° C., or up to 230° C. (e.g., as measured at theexternal surface of the electrochemical cell) without theelectrochemical cell experiencing thermal runaway. In some embodiments,the electrochemical cell can be operated at any of the temperaturesoutlined above without igniting. In some embodiments, theelectrochemical cells described herein can be operated at relativelyhigh temperatures (e.g., any of the temperatures outlined above) withoutexperiencing thermal runaway and without employing an auxiliary coolingmechanism (e.g., a heat exchanger external to the electrochemical cell,active fluid cooling external to the electrochemical cell, and thelike).

Inventive electrochemical cells can provide a high percentage of sulphurutilization, such as 60% or more, at a discharge rate of 10 hours orless.

A further aspect of the present invention is a method to manufactureelectrochemical cells. Said methods are hereinafter also referred to asinventive methods. One set of inventive methods comprises the followingsteps:

(1) providing lithium or a lithium alloy which may be deposited on asubstrate,

(2) depositing a solution of at least one organic polyethersulfone withat least one heteroatom containing (co)monomer in an organic solvent onsaid lithium or lithium alloy,

(3) adjusting the solvent content of polyethersulfone to a range of from0.01 to 25% by weight,

(4) treating said deposited polyethersulfone with at least one salt oflithium or sodium in at least one organic solvent.

Said steps are described in more detail below.

In step (1), lithium or a lithium alloy is provided. Lithium alloys havebeen described above.

The lithium or lithium alloy can be provided in any form, e.g., apowder. In some cases, the lithium or lithium alloy is provided in aform deposited on a substrate such as, e.g., a polymer.

In one embodiment, said substrates are selected from current collectorsand from polymer carriers.

Said substrate can be a polymer film, in some instances. Polymer filmscan be made of various polymers such as polyesters such as polyethyleneterephthalate, polysilicones (silicones), and siliconized polyesters.

In cases in which the lithium or lithium alloy is deposited on asubstrate, said lithium or lithium alloy can be deposited as a layer orfoil. In some embodiments, each layer or foil can have a thickness fromabout 2 μm to about 200 μm, from about 5 μm to about 50 μm, from about 2μm to about 35 μm, from about 5 μm to about 35 μm, or up to about 35 μm.

Deposition of lithium or lithium alloy can be performed by, e.g.,sputtering, thermal evaporation and condensation, jet vapour deposition,and LASER ablation.

In one embodiment of the present invention, in step (1), a substratewith lithium or lithium alloy and optionally ceramic material depositedthereon is provided. For instance, the ceramic material can be depositedin connection with the lithium. Ceramic materials have been describedabove. Ceramic material and lithium or lithium alloy can be depositedtogether, in some instances in alternating layers. For example, in someembodiments, ceramic material can be deposited on the lithium or lithiumalloy and/or ceramic material can be deposited between portions of thelithium or lithium alloy (e.g., between layers of lithium or lithiumalloy). In one embodiment of the present invention, up to ten layers oflithium or lithium alloy and up to ten layers of ceramic material can bedeposited alternatingly on said substrate, each layer having a thicknessin the range of from 0.1 to 25 μm.

In step (2), a solution of at least one polyethersulfone in a solventcan be deposited on lithium or a lithium alloy which has been depositedon the substrate. The depositing can be performed, e.g., by spraying,roller coating, dipping, casting, spin coating, printing by letterpress, doctor blade, ink-jet printing, screen printing, or web coating.

Polyethersulfone has been described above in detail, andpolyethersulfone can be deposited in pure form or as a blend with atleast one additional (co)polymer. The solution of polyethersulfone, orof polyethersulfone and additional (co)polymer, respectively, can have asolids content of from about 1% to about 50% by weight, or from about 5%to about 20% by weight. The solution of organic polyether sulfone (C)may additionally comprise an organic or inorganic filler (G) and/or a(co)polymer (F).

The solvent used to deposit the polyethersulfone (or another non-fluidmaterial in the electrolyte) can be selected from non-protichalogen-free organic solvents. In some embodiments, the solvent can beselected from cyclic or non-cyclic ethers, cyclic or non-cycliccarbonates, cyclic or non-cyclic acetals, cyclic or non-cyclic ketals,or cyclic or non-cyclic amides, and mixtures of two or more of theprevious. Other examples of suitable solvents that can be used todeposit polyethersulfone or any other non-fluid material in theelectrolyte include the solvents described above for use within thefinal electrochemical cell (e.g., the auxiliary material solventsdescribed above and organic solvent (D), respectively). In someembodiments, the solvent used to deposit polyethersulfone or anothernon-fluid material in the electrolyte (solvent (D1)) can be the samesolvent that is present within the assembled electrochemical cell(organic solvent (D)). In other cases, the solvent used to depositpolyethersulfone or another non-fluid material in the electrolyte (D1)can be different than the solvent present within the assembledelectrochemical cell (D).

In one embodiment of the present invention, the solvent used to depositpolyethersulfone or another non-fluid material in the electrolyte isselected from cyclic or non-cyclic organic amides, and the solventpresent within the assembled electrochemical cell is selected fromcyclic or non-cyclic ethers, cyclic or non-cyclic carbonates, and cyclicor non-cyclic acetals.

In step (3) of inventive method, the residual solvent content ofpolyether sulfone can be adjusted to be from about 0.01% to about 25% byweight, measured as a percentage of the sum of the masses of theresidual solvent and the polyether sulfone. Said adjustment can beachieved by evaporation, e.g. by heat treatment, in some cases underreduced pressure. Reduced pressure in the context of the presentinvention can be in a range of from about 1 to about 500 mbar.

The residual solvent content can be measured by thermogravimetricanalysis.

In step (4) of the inventive method, deposited polyethersulfone, in pureform or as blend at least one additional (co)polymer, will be treatedwith a solution of at least one salt of lithium (E) in at least oneorganic solvent (D). Solvent (D) can be selected from the solventsdescribed above as suited as organic solvent (D).

Salts have been characterized above. The concentration of salt insolvent can be from about 0.1 M to about 2.0 M, or from about 1.0 M toabout 1.2 M. Said treatment can be performed by, e.g., dipping, orspraying.

Steps (2), (3) and (4) of the inventive method can be performed atvarious temperatures. Steps (2) and (4) can be performed at ambienttemperature, in some embodiments.

In one embodiment of the present invention, step (3) of the inventivemethod can be performed at ambient temperature or at a temperature offrom about 30° C. to about 150° C., or from about 40° C. to about 70° C.

In one embodiment of the present invention, an additional step (5) isadded after steps (1) to (4). Additional step (5) comprises removal ofthe substrate from the lithium or the respective lithium alloy. Saidstep (5) can be carried out mechanically, in some instances.

In case the substrate whereon lithium or the respective lithium alloyhas been deposited is a siliconized polyester foil, step (5) isperformed particularly easy.

In one embodiment of the present invention, the inventive processadditionally comprises the step of

(6) crosslinking the deposited polyethersulfone.

In one embodiment of the present invention, an additional step (6) isadded after steps (1) to (4) and, optionally, step (5). Additional step(6) comprises cross-linking organic polyethersulfone alone or withfiller. Said cross-linking can be performed by thermal cross-linking orUV/vis irradiation, by γ-irradiation, or by electron beams. Saidcross-linking can be performed in the presence of one or morecross-linkers. In some cases in which cross-linking is performed byUV/vis irradiation, one can add a photoinitiator (e.g., at about 0.5-5%of the polymer) to improve the cross-linking reaction.

Instead of polysulfones other (co)polymers like PVOH and branchedpolyimide may be used in the method to manufacture electrochemical cellsdescribed above.

An anode/electrolyte combination manufactured according to the inventiveprocess described above can be combined with a cathode, and optionallywith a separator to form an electrochemical cell (e.g., a battery suchas a lithium sulfur battery). Optionally, further constituents such aselectrode terminal connections and a housing such as a box or a bag orpouch can be added to form an electrochemical cell.

Two or more inventive electrochemical cells can be combined to form abattery. An inventive battery contains at least two inventiveelectrochemical cells together with the necessary cable connections andwith a housing.

A further aspect of the present invention is a process for running amachine containing one or more inventive electrochemical cells or aninventive battery.

Suitable machines include transportation devices, such as aircraft,automobiles, locomotives, and ships. Due to the advantageousrechargeability (cycleability) of inventive electrochemical cells, highefficiency can be achieved. Furthermore, running said machines can alsoparticularly safe due to reduced thermal runaway problems.

U.S. Provisional Patent Application Ser. No. 61/376,559, filed Aug. 24,2010, and entitled “Electrolyte Materials for Use in ElectrochemicalCells,” is incorporated herein by reference in its entirety for allpurposes. In addition, a U.S. Utility Patent Application, filed on Aug.24, 2011, under attorney docket number S1583.70032US01, and entitled“Electrolyte Materials for Use in Electrochemical Cells” is alsoincorporated by reference herein in its entirety for all purposes.

EXAMPLES

The following examples are intended to illustrate certain embodiments ofthe present invention, but do not exemplify the full scope of theinvention.

All percentages are referring to percent by weight unless expresslystated otherwise.

The following materials were used:

Polyethersulfone (C.1) M_(w) 33,000 g/mol, M_(w)/M_(n)=4.5, methylatedpolycondensation product of

Polyethersulfone (C.2) M_(w) 38,500 g/mol, M_(w)/M_(n)=3.5, methylatedpolycondensation product of

Fillers:

(G.1) fumed silica commercially available as TS-720 from Cabot

(G.2) fumed silica commercially available as Aerosil® R812 fromEvonik-Degussa

(G.3) clay commercially available as Cloisite 30B

Separator (I.1): Tonen. Micorporous polyethylene; thickness: 9 μm; 270Gurley seconds.

Separator (I.2): Celgard. Triple layer(Polypropylene/Polyethylene/Polypropylene) micorporous separator;thickness 25 μm; 620 Gurley seconds.

Cathode (A.1): 55% sulfur, 20% XE-2 carbon, 20% Vulcan carbon, and 5%polyvinylalcohol binder with sulfur active material loading of 1.85mg/cm². Total cathode active area in the cell was about 90 cm².

All cycling experiments were performed under a pressure of 10 kg/cm².

Electrolyte 1:

Solution of 4 g lithium nitrate, 8 g lithiumbis-(trifluoromethylsulfon)imide, 1 g guanidinium nitrate, and 0.4 gpyridinium nitrate in 43.8 g 1,2-dimethoxy ethane and 43.8 g1,3-dioxolane.

Branched Polyimide (HPI.1) with Mw 1,700 g/mol prepared by the reactionof the dianhydride of 1,2,4,5-benzene tretracarboxylic acid withpolymeric 4,4′-diphenylmethane diisocyanate having an average of 2.7isocyanate groups per molecule, dynamic viscosity: 195 mPa·s at 25° C.,commercially availabe as Lupranat® M20W.

Example 1

This example outlines, according to one set of embodiments, themanufacture of an inventive electrochemical cell EC.1

A slurry was prepared from a solution of polyethersulfone (C.1) (10%wt.) and filler (G.1) (10% wt.) in diethyleneglycol dimethyl ether wascoated onto vacuum deposited lithium (VDL) on a web coater. The weightratio of polysulfone/silica was 7:3. The gel layer was dried in a gelcoater oven at 65-80° C. An anode (B.1) with a dry gel layer wasobtained. The resulting thickness of the dry gel layer was 7 μm. Atriple bi-cell with above anodes (B.1), separators (I.1) and cathodes(A.1) was assembled and filled with electrolyte 1. Inventiveelectrochemical cell EC.1 was obtained. Inventive electrochemical cellEC.1 displayed 1015 mAh/g sulfur specific capacity on the 5^(th)discharge. Inventive electrochemical cell EC.1 was cycled for 10 cyclesand went for a safety test. The inventive electrochemical cell EC.1 atfully charged conditions was ramped at 5° C./min without going intothermal runaway up to 230° C.

Comparative Example 1

A triple bi-cell with VDL anode, separator (I.1) and cathodes (A.1) wasassembled and filled with electrolyte 1. Comparative electrochemicalcell C-EC.2 was obtained. Comparative electrochemical cell C-EC.2displayed 982 mAh/g specific capacity on the 5^(th) discharge.Comparative electrochemical cell C-EC.2 was cycled for 10 cycles andwent for the safety test. Comparative electrochemical cell C-EC.2 wasramped at 5° C./min and went into thermal runaway at 140° C.

Example 2

This example describes, according to some embodiments, the manufactureof an inventive electrochemical cell EC.3.

A slurry prepared from a solution of polyethersulfone (C.1) (10% wt.)and filler (G.2) (10% wt.) in diethyleneglycol dimethyl ether was coatedonto VDL on a web coater. The weight ratio of polysulfone/silica was7:3. The gel layer was dried in a gel coater oven at 65-80° C. An anode(B.3) with a dry gel layer was obtained. The resulting thickness of thedry gel layer was 7 μm. A triple bi-cell with above anodes (B.3),separators (I.1) and cathodes (A.1) was assembled and filled withelectrolyte 1. Inventive electrochemical cell EC.3 was obtained.Inventive electrochemical cell EC.3 displayed 1025 mAh/g specificcapacity on the 5^(th) discharge. Inventive electrochemical cell EC.3was cycled for 10 cycles and went for the safety test. Inventiveelectrochemical cell EC.3 was ramped to 230° C. without going intothermal runaway.

Example 3

This example describes the manufacture of an inventive electrochemicalcell EC.4, according to one set of embodiments.

A slurry prepared from a solution of polyethersulfone (C.1) (10% wt.)and filler (G.3) (10% wt.) in diethyleneglycol dimethyl ether was coatedonto VDL on a web coater. The weight ratio of polysulfone/silica was1:1. An anode (B.4) with a dry gel layer was obtained. The gel layer wasdried in a gel coater oven at 65 80° C. An anode (B.4) with a dry gellayer was obtained. The resulting thickness of the dry gel layer was 7μm. A triple bi-cell (EC.4) with above anodes (B.3), separators (I.2)and cathodes (A.1) was assembled and filled with electrolyte 1.Inventive electrochemical cell EC.4 was obtained. Inventiveelectrochemical cell EC.4 displayed 1019 mAh/g specific capacity on the5^(th) discharge.

Example 4

This example describes, according to one set of embodiments, themanufacture of an inventive electrochemical cell EC.5.

A slurry prepared from a solution of polyethersulfone (C.1), filler(G.1) and dipropylenglycol diacrylate with photoinitiator indiethyleneglycol dimethyl ether was coated onto vacuum deposited lithium(VDL) on a web coater and irradiated with UV light in argon atmosphere.The following properties were observed: Weight ratio(C.1)/(F.1)/diacrylate=49.3/21.1/29.6; total solids content: 10% byweight. An anode (B.5) with a dry gel layer was obtained. The resultingthickness of dry gel layer was 5 μm. A triple bi-cell with above anodes(B.5), separators (I.2) and cathodes (A.1) was assembled and filled withelectrolyte 1. Inventive electrochemical cell EC.5 was obtained.Inventive electrochemical cell EC.5 displayed 1068 mAh/g specificcapacity on the 5^(th) discharge.

Example 5

This example describes the manufacture of an inventive electrochemicalcell EC.6, according to some embodiments.

A slurry prepared from a solution of polyethersulfone (C.1) and filler(G.1) in 1,4-dioxane was coated onto vacuum deposited lithium (VDL) on aweb coater and irradiated with UV light in argon atmosphere. The weightratio of polysulfone/silica was 7:3. The total solids content was about10% by weight. Drying was achieved via UV light exposure at atemperature of 40-65° C. An anode (B.6) with a dry gel layer wasobtained. The resulting thickness of dry gel layer was 6 μm. A triplebi-cell with above anodes (B.6), separators (I.2) and cathodes (A.1) wasassembled and filled with electrolyte 1. Inventive electrochemical cellEC.6 was obtained. Inventive electrochemical cell EC.6 displayed 1025mAh/g specific capacity on the 5^(th) discharge.

Example 6

This example describes the manufacture of polymer electrolyte gelcomprising HPI.1.

A solution comprising 30 wt.-% of HPI.1 in DMAc was prepared and coatedby a doctor blade onto a lithium electrode comprising vacuum depositedlithium (VDL) on the top surface (example 6.a) and on Ni-electrodes(example 6.b, for measuring the conductivity, see example 8) at 80° C.for 2 h and was then dried for 24 h in a vacuum oven at the sametemperature. Subsequently the films were immersed in electrolyte 1 for24 to 48 h.

Example 7

This example describes the measurement of the hardness of a lithiumelectrode comprising vacuum deposited lithium (VDL) on the top surfaceand the lithium electrode comprising vacuum deposited lithium (VDL) onthe top surface coated with HPI.1 and swollen with electrolyte 1 fromexample 6.a. The hardness was measured with an AFM device (Veeco, N.Y.,USA) by indentation with a Berkovich-type indenter (“Triposcope”HYSITRON, Minn., USA) with a load of 1000 μN and a depth of indentationof about 2000 nm. The hardness was calculated from the E-module. Thehardness of the uncoated lithium was 9 MPa, the hardness of the lithiumcoated by the polymer gel electrolyte of example 6.a was 80 MPa.

Example 8

This example describes the measurement of the conductivity of thepolymer gel electrolyte from example 6.b. The conductivity wasdetermined by measuring the impedance with an impedance measurement unit(model IM6ex by Zahner (Germany)) at a voltage of 5 mV (AC) and afrequency of from 1 MHz to 10 HZ. The conductivity was 7.4×10⁻⁴ S/cm.

While several embodiments of the present invention have been describedand illustrated herein, those of ordinary skill in the art will readilyenvision a variety of other means and/or structures for performing thefunctions and/or obtaining the results and/or one or more of theadvantages described herein, and each of such variations and/ormodifications is deemed to be within the scope of the present invention.More generally, those skilled in the art will readily appreciate thatall parameters, dimensions, materials, and configurations describedherein are meant to be exemplary and that the actual parameters,dimensions, materials, and/or configurations will depend upon thespecific application or applications for which the teachings of thepresent invention is/are used. Those skilled in the art will recognize,or be able to ascertain using no more than routine experimentation, manyequivalents to the specific embodiments of the invention describedherein. It is, therefore, to be understood that the foregoingembodiments are presented by way of example only and that, within thescope of the appended claims and equivalents thereto, the invention maybe practiced otherwise than as specifically described and claimed. Thepresent invention is directed to each individual feature, system,article, material, kit, and/or method described herein. In addition, anycombination of two or more such features, systems, articles, materials,kits, and/or methods, if such features, systems, articles, materials,kits, and/or methods are not mutually inconsistent, is included withinthe scope of the present invention.

The indefinite articles “a” and “an,” as used herein in thespecification and in the claims, unless clearly indicated to thecontrary, should be understood to mean “at least one.”

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases. Other elements may optionallybe present other than the elements specifically identified by the“and/or” clause, whether related or unrelated to those elementsspecifically identified unless clearly indicated to the contrary. Thus,as a non-limiting example, a reference to “A and/or B,” when used inconjunction with open-ended language such as “comprising” can refer, inone embodiment, to A without B (optionally including elements other thanB); in another embodiment, to B without A (optionally including elementsother than A); in yet another embodiment, to both A and B (optionallyincluding other elements); etc.

As used herein in the specification and in the claims, “or” should beunderstood to have the same meaning as “and/or” as defined above. Forexample, when separating items in a list, “or” or “and/or” shall beinterpreted as being inclusive, i.e., the inclusion of at least one, butalso including more than one, of a number or list of elements, and,optionally, additional unlisted items. Only terms clearly indicated tothe contrary, such as “only one of” or “exactly one of,” or, when usedin the claims, “consisting of,” will refer to the inclusion of exactlyone element of a number or list of elements. In general, the term “or”as used herein shall only be interpreted as indicating exclusivealternatives (i.e. “one or the other but not both”) when preceded byterms of exclusivity, such as “either,” “one of,” “only one of,” or“exactly one of.” “Consisting essentially of,” when used in the claims,shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements. This definition also allows that elements may optionally bepresent other than the elements specifically identified within the listof elements to which the phrase “at least one” refers, whether relatedor unrelated to those elements specifically identified. Thus, as anon-limiting example, “at least one of A and B” (or, equivalently, “atleast one of A or B,” or, equivalently “at least one of A and/or B”) canrefer, in one embodiment, to at least one, optionally including morethan one, A, with no B present (and optionally including elements otherthan B); in another embodiment, to at least one, optionally includingmore than one, B, with no A present (and optionally including elementsother than A); in yet another embodiment, to at least one, optionallyincluding more than one, A, and at least one, optionally including morethan one, B (and optionally including other elements); etc.

In the claims, as well as in the specification above, all transitionalphrases such as “comprising,” “including,” “carrying,” “having,”“containing,” “involving,” “holding,” and the like are to be understoodto be open-ended, i.e., to mean including but not limited to. Only thetransitional phrases “consisting of” and “consisting essentially of”shall be closed or semi-closed transitional phrases, respectively, asset forth in the United States Patent Office Manual of Patent ExaminingProcedures, Section 2111.03.

What is claimed is:
 1. An article, comprising: an electrochemical cell,comprising: a first electrode comprising lithium metal; a secondelectrode; an electrolyte comprising a solvent, a lithiumbis-oxalatoborate salt, a lithium nitrate salt, and a further lithiumsalt, wherein a total salt content in the solvent is between 0.5 M and 2M; and a ceramic material deposited on the lithium metal.
 2. The articleof claim 1, wherein the electrochemical cell further comprises aguanidinium nitrate salt.
 3. The article of claim 1, wherein theelectrochemical cell further comprises a pyridinium nitrate salt.
 4. Thearticle of claim 1, wherein the electrolyte comprises a first componentand a second component.
 5. The article of claim 1, wherein theelectrolyte is a polymer gel electrolyte.
 6. The article of claim 1,wherein the electrolyte has a yield strength greater than a yieldstrength of lithium metal.
 7. The article of claim 1, wherein aconcentration of the oxalatoborate-containing salt in the electrolyte isfrom about 0.5 M to about 2.0 M.
 8. The article of claim 1, wherein theelectrolyte has a salt concentration of about 0.8 M to about 1.2 M. 9.The article of claim 1, wherein the electrolyte has a salt concentrationof about 0.7 M to about 1.5 M.
 10. The article of claim 1, wherein thesecond electrode comprises sulfur.
 11. The article of claim 1, whereinthe electrolyte is a liquid.
 12. The article of claim 1, wherein theelectrolyte comprises a polyethersulfone.
 13. The article of claim 1,wherein the electrochemical cell further comprises a separatorpositioned between the first electrode and the second electrode.
 14. Thearticle of claim 1, wherein the ionic conductivity of the electrolyte isat least 5×10⁻⁶ S/cm at room temperature.
 15. The article of claim 1,wherein the electrolyte comprises a carbonate.
 16. An article,comprising: an electrochemical cell, comprising: a first electrodecomprising lithium metal; a second electrode; an electrolyte comprisinga solvent, a lithium bis-oxalatoborate salt, a lithium nitrate salt, andLiPF₆, wherein a total salt content in the solvent is between 0.5 M and2 M; and a ceramic material deposited on the lithium metal.